1. Field of Invention
This invention relates to fluid ejection systems and methods.
2. Description of Related Art
Fluid ejection systems, such as ink jet printers, have at least one fluid ejector that directs droplets of fluid towards a receiving medium. Within the fluid ejector, the fluid may be contained in a plurality of channels. Energy pulses are used to expel the droplets of fluid, as required, from orifices at the ends of the channels.
A carriage-type thermal fluid ejector system is described in U.S. Pat. No. 4,638,337 (""337 Patent). The system disclosed in the ""337 patent has a plurality of printheads, each with its own fluid tank cartridge, mounted on a reciprocating carriage. The channel nozzles in each fluid ejector are aligned perpendicular to the line of movement of the carriage. A swath of information is printed on a stationary receiving medium as the carriage is moved in one direction. The receiving medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath. The carriage is then moved in the reverse direction to eject another swath of fluid.
In conventional systems, a stitching method is employed that stitches together a first one of the swaths and a second one of the swaths. The stitching method, at some specific point in the overlap region, ejects fluid to satisfy specific pixel densities within the overlap region in the first swath, and subsequently ejects fluid to satisfy specific pixel densities within the overlap region in the second swath.
In U.S. patent application Ser. No. 09/232,636, incorporated herein by reference in its entirety, a multi-sensor scanning system or image processing system is disclosed which includes a plurality of sensors. Each sensor scans a portion of a document to produce image data. Each of the sensors overlap adjacent sensors and the sensors thus produce overlapped image data. The image data is stitched together to form a complete image by performing a weighted averaging over the overlapped image data. The weighted averaging may be linear or non-linear.
Although the exemplary systems and methods according to this invention provide examples of stitching overlapping swaths using xe2x80x9cfluid ejection,xe2x80x9d it should be appreciated that the systems and methods according to this invention can use any material that can be propelled onto a receiving medium or transfer media. For example, the systems and methods according to this invention can be used with a system where the fluid is derived from a solid material.
It should also be appreciated that various arrangements of multiple fluid ejectors can be used that require an overlapping architecture. While scanning carriage printers are one obvious example, larger higher productivity printing systems using multiple heads can be conceived. These architectures may have multiple heads per color or multiple many-color heads. Moreover, these heads can range from small devices to partial width arrays to large arrays for large format devices. Finally, these heads may move, but also may be fixed to the frame or sub-frame of the imaging system.
As described above, fluid ejection systems usually use a single fluid ejector that prints a corresponding number of swaths, or an array of fluid ejectors that print a swath. Thus, the fluid ejection system""s productivity is limited to the size of the fluid ejectors used. During printing, while the fluid ejectors print a swath, productivity increases if the fluid ejectors move a full swath width relative to the previous swath. Thereafter, the fluid ejectors print an additional swath.
However, pattern quality of the ejected fluid when using this process is reduced as the opportunity to place fluid drops in a given location is limited to one pass of the fluid ejector. Another problem occurs in that stitch errors occur between each swath as the ejected drops in a first swath fail to align with the ejected drops in adjacent second swath. The stitch errors can occur whenever a subsequent drop ejected by the fluid ejector in one swath is displaced in any direction relative to the position that such a drop should occupy on the receiving medium relative to a previous drop ejected by the fluid ejector in the adjacent swath.
One technique for dealing with this problem is to overlap adjacent swaths. However, overlapping the swaths increases the number of mechanical stitching defects created on the receiving medium, and, in addition, oversized overlaps can also negatively impact productivity. This problem is especially present when multiple fluid ejectors for a single fluid are placed on a single carriage or otherwise are used together in a single fluid ejection system. These multiple fluid ejectors can be staggered on the carriage or arranged in a line.
This invention provides systems and methods that mask the stitching defects created between overlapping swaths.
This invention separately provides systems and methods that improve the quality of an image on a receiving medium by reducing stitching defects in missing printed data.
This invention separately provides systems and methods that improve the quality of an image on a receiving medium by reducing the defects in image data that occurs at a point in the image where the brightness and/or gray level rapidly changes.
This invention separately provides systems and methods that eject a successively smaller amount of fluid on the last few lines of a first swath of a receiving medium, while subsequently ejecting a successively larger amount of fluid on the first few lines of an adjacent swath.
The invention provides systems and methods that, during a first swath, eject fluid for only a first portion of pixels, in an overlapping region, while a second portion of pixels is skipped over, and that, during an adjacent second swath eject fluid for only the second portion of pixels, while the first portion of pixels is skipped over.
In various exemplary embodiments of the fluid ejection system and methods according to this invention, overlapping swaths are stitched together by distributing the fluid ejection pattern between the overlapping swaths within the overlapped region.
In various exemplary embodiments, the fluid ejection system uses fluid ejectors that allow the size or number of drops ejected for each image pixel to be closely controlled. In these systems, because the amount of fluid can be controlled, the amount of fluid within each pixel of an overlapping region can be distributed between the two overlapping swaths. That is, the fluid ejection pattern can be controlled and intermediate density regions can be created by distributing the amount of fluid within a region between two fluid ejector heads or between two swaths generated by the same fluid ejector head. The distribution can be linear or non-linear.
In various other exemplary embodiments of the fluid ejection system and methods according to this invention, overlapping swaths are stitched together by randomly or pseudo-randomly varying a stitch location within the overlapped region between two overlapping fluid ejector heads or between two swaths generated by the same fluid ejector head. In this case, a stitch location is randomly or pseudo-randomly varied in the slow scan direction.
These and other features and advantages of this invention are described in or are apparent from the detailed description of various exemplary embodiments of the systems and methods according to this invention.